1.32 million sq. miles

NASA

Arctic sea ice melts to its lowest extent. The dotted yellow line indicates the average area from 1979 to 2000

That’s the estimated minimum extent for the Arctic sea ice this summer, reached on Sept. 16, according to scientists at the National Snow and Ice Data Center (NSIDC). It breaks the record for the lowest ever summer extent in the satellite record, beating 2007 by an area equal to the size of Texas. Though the Arctic sea ice—which melts and reforms each summer and winter—usually reaches its lowest extent in mid-September, this year actually broke the record even before the end of the melting season. The fact that the ice kept melting at high rates late into the summer is even more surprising. “The strong late season decline is indicative of how thin the ice cover is,” NSIDC scientist Walt Meier said in a statement. “Ice has to be quite thin to continue melting away as the sun goes down and fall approaches.”

As the summer ends and the long Arctic winter commences, the sea ice will reform, but every major melt season like this one flushes out more of the old, thick multi-year ice, replacing it with thin layers that will melt that much more easily next summer. If so, that would continue a long-term melting trend that dates back at least until satellite records of the Arctic began to be kept in 1979. This year’s minimum extent is 50% smaller than the 1979 to 2000 average, which underscores just how much sea ice has collapsed over the past decade.

The question now is whether that trend will continue—and how soon the Arctic will become ice-free. That’s a loaded question in climate science, but some researchers worry that the Arctic itself could become ice-free—during the summer at least—as soon as the end of the decade. That was one projection made by Wieslaw Maslowski, an Arctic expert at the Naval Postgraduate School, at a Greenpeace panel on the Arctic and climate change that I chaired yesterday morning. Whether or not that prediction comes true, it’s clear that the Arctic—the Last Frontier—is becoming the first frontier of climate change. And as Dan Lashof of the Natural Resources Defense Council said in a statement today: “What happens in the Arctic doesn’t stay in the Arctic.”